Abstract
The self-assembling properties of hydrophobically modified (HM) telechelic poly(N-isopropylacrylamides) (PNIPAM) were studied in aqueous solutions of concentration ranging from 0.1 to 11 g L-1 by fluorescence spectroscopy, using N-phenyl-1-naphthylamine as a probe, and by static (SLS) and dynamic (DLS) light scattering over a temperature domain encompassing their cloud point (Tcp) and coil-to-globule transition temperature (TM). The telechelic HM−PNIPAM samples bear n-octadecyl termini, and their molar mass (Mn) ranges from 12 000 to 49 000 g mol-1 with a polydispersity index lower than 1.20. In cold aqueous solution, the HM−PNIPAM samples associate in the form of flower micelles (10.8 < RH < 17.5 nm, RG/RH ≅ 1.3−1.5) consisting of ≅16−27 polymer chains, depending on their molecular weight. In solutions heated under equilibrium conditions above TM, individual flower micelles with collapsed loops associate to form stable mesoglobules (RG/RH ∼ 0.80) comprising a few hundreds chains with a more rigid and more polar interior than the hydrophobic core of hydrated flower micelles. The size of the mesoglobules increases with increasing polymer concentration (19 < RH < 115 nm), but in all cases the mesoglobule size distributions are narrower than those of the corresponding polymer micelles in cold solutions.
Published Version
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